gfgfg PLANT BOARD
November 1952 E-850
United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine
EXPERIMENTS IN PREVENTING THE BUILD-UP OF INSECTS
IN NEWLY HARVESTED WHEAT
By Gailen D. White
Division of Stored Product Insect Investigations
An effective method of preventing the build-up of insects in newly
harvested wheat has long been needed. Normally wheat is not infested
in the field, but after it is harvested insects may begin an infestation
by moving into the wheat from hiding places in the storage bin such as
cracks or tunnels, or from waste grain, feed rooms, and other nearby
sources. It has been observed that stored-grain insects can multiply
themselves more than 40 times in farm -stored wheat during the first
4 months of storage in wooden farm granaries.
After the wheat is harvested, the insects have from 3 to 6 months
in which they can multiply rapidly before winter temperatures cool the
wheat. A means to prevent the increase of insects in the grain during
the post-harvest period is therefore highly desirable.
Dusts have been employed for the protection of seed for many years,
but the materials used are not suitable for grain intended for feed or
food, because of their toxic nature. Recently dusts containing pyrethrum
and similar materials have been considered, since they would not be
harmful to animals or humans in the amounts used. It is not feasible to
add inorganic diluents to commercial stocks of grain, since they tend to
lower the grade, being indistinguishable from lime or other foreign
matter causing down-grading. It has also been found that insecticidal
sprays applied to the walls and floors of wooden storage bins before
being filled are very helpful in reducing initial infestation from these
Therefore, in the summer of 1951 tests were made in farm bins in
Reno County, Kans., to determine the effectiveness of (1) insecticidal
sprays applied to interior walls of wooden farm granaries, (2) fumigants
applied late in August, and (3) synergized-pyrethrum dusts in preventing
population build-up in newly harvested wheat. Where bins were sprayed,
a water emulsion containing 0.2 percent of pyrethrins and 2 percent of
piperonyl butoxide was applied at the rate of 1 gallon per 1, 000 square
feet of wall area, or a 2.5-percent water suspension of DDT applied at
the rate of 2 gallons per 1,000 square feet. The bins in the fumigation
series were fumigated with a 3:1 mixture of ethylene dichloride and
carbon tetrachloride, applied at the rate of 6 gallons per 1,000 bushels
of wheat. The protectant dust contained 0.08 percent of pyrethrins and
1.1 percent of piperonyl butoxide— 'in a wheat-dust diluent. It was applied
at the rate of 75 pounds per 1,000 bushels.
The tests were grouped into six series as follows:
1. Control, no treatment (19 bins).
2. Fumigation late in August (12 bins).
3. DDT spray on walls (9 bins)
4. Pyrethrum -piperonyl butoxide spray on walls (8 bins).
5. Pyrethrum -piperonyl butoxide dust in wheat (9 bins).
6. Pyrethrum-piperonyl butoxide spray on walls, pyrethrum -
piperonyl butoxide dust in wheat (7 bins).
In series 5 the wheat was treated with a special applicator attached
to a portable auger-type elevator, by which the rate of dust flow was
In series 6 the dust was applied to the wheat by the individual farmers
as the bins were filled with whatever equipment they had at hand. Some
of these bins were filled by auger-type grain elevators, and the dust was
introduced as the grain was dumped from the truck to the auger so that
the mixing of dust with grain was done by the auger. In other bins the
dust was added to the grain stream as it was dumped from the truck into
the pit of a stationary bucket-type farm grain elevator. After the bins
were filled with the treated grain, the grain surfaces were "capped" to
a depth of 3 inches with the dust applied at twice the experimental rate,
or 150 pounds per 1,000 bushels.
The original moisture content was determined for each bin. Once a
month each bin was sampled at three locations with a 5 -foot grain trier,
or probe. The total number of insects present regardless of species
was recorded for each sample. For series 1 to 5 observations were
terminated in September, since the grain was either sold or used for
seeding purposes. It was possible to take October records for series 6.
Control bins were sampled to indicate the normal increase in insect
population over this period. The September population levels were used
as the measure of effectiveness of the various treatments, since insect
populations in farm- stored grain in Kansas have usually reached their
peak by that time.
1/ This material was furnished by U. S. Industrial Chemicals Co.
- 3 -
The average original moisture content and the average number of
insects per 1,000 grams of wheat for each series of bins are given in
table 1. The bins in the control series developed the greatest population,
i.e., 41.4 insects per 1,000 grams. The populations in all the treated
bins were significantly lower than in the control series at the 1 percent
level of significance.
The bins fumigated late in August had the lowest population in
September. Those treated with dust gave the next best results. Insect
populations were not significantly lower in dusted wheat in sprayed bins
than in those receiving dust only. The October sampling in series 6
showed an increase in population, but this increase was entirely in one
bin in the series. The bin receiving DDT wall spray averaged consider-
ably lower in insect population than the one sprayed with the pyrethrum-
piperonyl butoxide mixture.
Samples of dust-treated wheat from bins in series 5 and 6 were
submitted to the Kansas State Grain Inspection Department for grading.
No change in grade resulted from the use of this dust.
Table 1. --Average moisture content and numbers of insects found in
wheat stored in wooden farm bins in experimental series, Reno,
County, Kans., 1951
Number of insects per
1,000 grams of wheat in--
Fumigation in August
DDT spray on walls
spray on walls
dust in wheat
spray on walls;
dust in wheat
1/ Before fumigation.
UNIVERSITY OF FLORIDA
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